OBJECTIVE: The objective of this study was to quantify the effects of a 4 week, supervised, high-intensity interval training (HIIT) on intrahepatic triglyceride content (IHTG, percentage), cardiorespiratory fitness (CRF), and cardiometabolic markers in adolescents with obesity. METHODS: A total of 40 adolescents (age 13 to 18 y, BMI 36.7 +/- 5.8 kg/m2) at risk for metabolic dysfunction-associated steatotic liver disease (MASLD) based on obesity and elevated Fibroscan measured controlled attenuation parameter (CAP) scores were randomized to HIIT three times a week for 4 weeks (n = 34) or observation (control; n = 6). Liver magnetic resonance imaging proton-density fat-fraction (MRI-PDFF), CAP, oral glucose tolerance test, serum alanine aminotransferase, dual-energy x-ray absorptiometry, and CRF tests were performed before and after intervention. Within- and between-group differences were compared. RESULTS: A total of 13 (38%) and 4 (66%) children had MASLD by MRI-PDFF (IHTG >= 5%) in the HIIT and control groups, respectively. The implemented HIIT protocol had no impact on CRF or IHTG (baseline 5.26%, delta -0.31 percentage points, 95% confidence interval (CI) -0.77 to 0.15; p = 0.179), but it decreased the 2 h glucose concentration (baseline 116 mg/dL, delta -11 mg/dL; 95% CI -17.6 to -5.5; p < 0.001). When limiting the analysis to participants with MASLD (n = 17), HIIT decreased IHTG (baseline 8.81%, delta -1.05 percentage points, 95% CI -2.08 to -0.01; p = 0.048). Between-group comparisons were not different. CONCLUSIONS: The implemented exercise protocol did not reduce IHTG, but it led to modest improvement in markers of cardiometabolic health.

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